Fibres comprising copolymers of propylene with a low content of 1-hexene are already known in the art.
International patent application WO-A1-95/32091 discloses fibres comprising a homo or copolymer of propylene having a melting point in the range from 100° C. to 145°. The applicant discovered that better results in some application can be achieved by using copolymer having higher melting point.
International patent application WO-A1-96/27041 discloses fabrics with a very pleasing hand. Said performance is obtained with fibres made from copolymers of propylene and an α-olefin, such as ethylene, 1-butene and 1-hexene. The 1-hexene derived unit content is from 2 wt % to 5 wt % and the preferred melt flow rate (MFR) ranges from 10 to 50 dl/10 min. The applicant found that in is possible to improve the feature of the fibres by selecting among other features of the copolymer a sub MFR range, said MFR range being obtained by visbreaking the starting polymer.
International patent application WO-A1-2005/059210 discloses fibres for thermal bonding applications made of semicrystalline random copolymers of propylene with 1-hexene having a low degree of modification of the polymer. The amount of 1-hexene ranges from 1.5 to less than 3 wt % with respect to the total weight of the copolymer. The said copolymers possess a value of melt flow rate (MFR) ranging from 4 to 35 g/10 min, preferably from 8 to 20 g/10 min. In the example given, the said copolymer comprises an amount of 1-hexene of 2.9 wt % and shows a melt index of 10.1 dg/min. The applicant found that is possible to improve the properties of said fibres by fine tuning the properties of the starting copolymer and subjecting it to a visbreaking process.